The probable cause of the contact between self-discharging bulk carrier American Mariner (IMO 7812567) and the Munuscong Channel Junction Light was O-ring-type material debris in the steering gear system’s hydraulic oil. This became lodged within a control motor, which caused it to seize. That in turn caused the rudder to lock in position, the US National Transportation Safety Board (NTSB) has found.
On March 28th 2024 at 00:18 local time the 730ft-long self-unloading bulk carrier struck the Munuscong Channel Junction Light near Sault Ste Marie. Michigan, north USA.
It was transiting upbound in the St. Marys River, about 25 miles south of Sault Ste. Marie, when the steering failure occurred. The vessel hit the Munuscong Channel Junction Light, a 31ft-diameter cylindrical concrete structure with a navigation aid on top.
The vessel began taking on water, but pumps were deployed to stabilize the flooding. None of the 18 crewmembers on board were injured, and no pollution was reported.
Damage to the vessel was estimated at $800,750, while damage to the Munuscong Channel Junction Light was estimated at $1.25m for repairs.
Initial underwater scans performed by the US Army Corps of Engineers indicated damage to the seabed foundation and underwater structure of the Munuscong Channel Junction Light, which caused the structure to lean from its originally constructed orientation.
As of the date of the NTSB report, repairs have not been made to the Munuscong Channel Junction Light.
The vessel suffered damage to the hull plating and internal framing below the waterline to the forepeak tank and the no. 1 port ballast tank.
The American Mariner was on its maiden voyage of the season after completing winter maintenance, which included the installation of a new steering control system. During the voyage, the crew noticed intermittent steering system alarms but could not identify their cause, as the rudder appeared to be responding correctly to commands.
Post-incident investigation revealed that the vessel’s No. 1 control motor, responsible for controlling the main hydraulic pump’s stroke, had failed. Upon disassembly, technicians discovered black, pliable debris lodged between the control motor’s rotating gears, preventing proper operation. The steering system returned to normal functionality after the installation of a replacement control motor.
Electronic technicians later recalibrated the steering control system, which resolved the alarm issues, suggesting there were also problems with the calibration parameters of the newly installed control system.
The Munuscong Channel Junction Light serves as a critical navigational aid in the St Marys River.
1980-built, USA-flagged, 15,396 gt American Mariner is owned and managed by American Steamship Co of Williamsville, NY, USA. It is entered with Steamship Mutual (Americas Syndicate) on behalf of American Steamship Co.
https://www.ntsb.gov/investigations/AccidentReports/Reports/MIR2518.pdf